Mediators and mechanisms of change in internet- and mobile-based interventions for depression: A systematic review

The efficacy of Internet- and mobile-based interventions (IMIs) for depression in adults is well established. Yet, comprehensive knowledge on the mediators responsible for therapeutic change in these interventions is pending. Therefore, we conducted the first systematic review on mediators in IMIs for depression, investigating mechanisms of change in interventions with different theoretical backgrounds and delivery modes (PROSPERO CRD42019130301). Two independent reviewers screened references from five databases (i.e., Cochrane Library, Embase, MEDLINE/PubMed, PsycINFO and ICTRP), selected studies for inclusion and extracted data from eligible studies. We included 26 RCTs on mediators in IMIs for depression (6820 participants), rated their risk of bias and adherence to methodological quality criteria for psychotherapy process research. Primary studies examined 64 mediators, with cognitive variables (e.g., perceived control, rumination or interpretation bias) being the largest group of both examined (m = 28) and significant mediators (m = 22); followed by a range of other mediators, including mindfulness, acceptance and behavioral activation. Our findings might contribute to the empirically-informed advancement of interventions and mental health care practices, enabling optimized treatment outcomes for patients with depression. Furthermore, we discuss implications for future research and provide methodological recommendations for forthcoming mediation studies with more pertinent designs, allowing for inferences with higher causal specificity.